Runoff generation in a pre-alpine catchment: A discussion between a tracer and a shallow groundwater hydrologist

Abstract

Runoff generation mechanisms vary between catchments and despite decades of research in many catchments, these mechanisms are still not fully understood. In this paper, runoff generation mechanisms in the steep pre-alpine catchments in the Alptal, Switzerland, are discussed. These fast responding catchments are characterized by low permeability soils on top of flysch bedrock. In combination with the high and frequent precipitation, this results in predominantly wet conditions. In many areas, the water table is close to the surface. We review the main results of recent (2009-2016) studies in these catchments that used isotope, stream chemistry and hydrometric data. These field studies focused on the spatial and temporal patterns in groundwater levels, spatial patterns in the isotopic composition and chemistry of streamflow during baseflow conditions, as well as the responses of streamflow and its isotopic composition during rainfall events. The combined results of these studies highlight the establishment of connectivity of areas with a different topographic position and areas with a different land use during rainfall events. They also show the importance of flow in higher conductivity near surface soil layers for runoff generation, as well as the frequent occurrence of surface runoff. Spatial differences in groundwater dynamics are related to topography. Streamflow responses are mainly affected by the rainfall characteristics; differences in streamflow and hydrochemistry between catchments with different portions of forest, meadows and wetlands, were relatively small. However, variations in the chemistry of baseflow along stream reaches within a catchment were considerable. Above all, these studies highlight the value of combining data on spatial patterns of groundwater levels and stream chemistry with long term data on streamflow to derive a more complete picture of the dominant runoff generation mechanisms.

Spatiotemporal variability in hydrochemistry of shallow groundwater in a small pre‐alpine catchment: The importance of landscape elements

“…20000090712703): Swiss Federal Office of Topography. Reproduced with permission of Swisstopo (BA18702) Stähli, & Seibert, 2018). Streamflow and groundwater levels respond quickly to rainfall (Fischer, Rinderer, Schneider, Ewen, & Seibert, 2015;Rinderer, van Meerveld, Stähli, & Seibert, 2015).…”

“…Most of the streams are not deeply incised and have almost no riparian zone (Hagedorn, Schleppi, Waldner, & Flühler, 2000). Soil depth ranges from 0.5 m at the ridge sites to more than 2.5 m in depressions and is weakly related to slope (van Meerveld et al, 2018). The soils consist mainly (>85%) of clay and silt (Schleppi et al, 1998).…”

“…Precipitation is relatively evenly distributed throughout the year (Feyen, Wunderli, Wydler, & Papritz, ). During the snow‐free season (June to October), it rains on average every second day (van Meerveld, Fischer, Rinderer, Stähli, & Seibert, ). Streamflow and groundwater levels respond quickly to rainfall (Fischer, Rinderer, Schneider, Ewen, & Seibert, ; Rinderer, van Meerveld, Stähli, & Seibert, ).…”

“…Soil depth ranges from 0.5 m at the ridge sites to more than 2.5 m in depressions and is weakly related to slope (van Meerveld et al, ). The soils consist mainly (>85%) of clay and silt (Schleppi et al, ).…”

The relevance of hydrological research in small catchments – A perspective from long-term monitoring sites in Europe

“…Most of the contributions focus on understanding of runoff generation mechanisms in the studied environments, using various types of data (hydrometric data, isotopes, stream chemistry) and approaches (analysis of thresholds, hysteresis, hydrological connectivity, controlling factors, and hydrological modeling). They also show the value of having a dense measurement network and applying complementary techniques to better define a conceptual model of runoff generation processes (van Meerveld., 2018;Zuecco et al, 2018). Some contributions also consider associated hydrological processes including rainfall partitioning and forest transpiration (Llorens et al, 2018), biochemical cycles (Gascuel-Odoux et al, 2018), and sediment transport (Llorens et al, 2018;Rodríguez-Caballero et al, 2018).…”